1. Field of the Invention
The present invention relates to a data transmission method for reducing the effect of electromagnetic interference and a data transmission device with the reduced effect of electromagnetic interference. More particularly, the present invention relates to a data transmission method and device used in a liquid crystal display (LCD) circuit for reducing the electromagnetic interference intensity generated from data lines.
2. Description of the Related Art
When electrical and electronic devices are operated, they often emit and radiate electromagnetic radiation that interferes with other electronic devices"" operations. For example, the electromagnetic radiation generated from other electrical and electronic devices may interfere with the operation of televisions, cordless phones, computers, and pagers, resulting in deteriorating the performance of these devices. This phenomenon is typically called electromagnetic interference (EMI), which is a critical concern for the design of electrical and electronic devices. Therefore, the U.S. Federal Communications Commission (FCC) has established a set of standards regarding EMI, which regulate electrical and electronic circuits, devices, and products. These regulations state that the EMI emissions of electronic circuits, devices and products should not be larger than the standard defined by the FCC in order to prevent the electrical and electronic circuits, devices, and products from influencing the operations of other electrical and electronic circuits, devices, and products.
Similarly, an LCD circuit is also subject to the effect of EMI when in operation. Hereafter a conventional LCD circuit structure and the EMI effect occurring therein are explained in conjunction with the accompanying diagrams.
FIG. 1 is a schematic diagram showing a conventional LCD circuit structure. Referring to FIG. 1, the conventional LCD circuit includes an ixc3x97j pixel array 11, an X driving circuit 12 electrically connected to the ixc3x97j pixel array 11, a Y driving circuit 13 electrically connected to the ixc3x97j pixel array 11, and a controller 14 electrically connected to the X driving circuit 12. More specifically, the ixc3x97j pixel array 11 is composed of ixc3x97j pixels (not shown). The X driving circuit 12 is composed of i driving units X1, X2, . . . , Xi, in which each of the driving units X1, X2, . . . , Xi, is driven by a clock signal CK and a data signal is sent to the pixel array 11 through a corresponding data line L1, L2, . . . , or Li, respectively. In addition, the Y driving circuit 13 is composed of j driving units Y1, Y2, . . . , Yj, in which each of the driving units Y1, Y2, . . . , Yj, sends a scanning signal to the ixc3x97j pixel array 11 through a corresponding scanning line S1, S2, . . . , or Sj, respectively. Furthermore, through a data bus, the controller 14 sends both of data signals D1 to Di and the clock signal CK to the X driving circuit 12.
In the above-mentioned conventional LCD circuit, the transmission frequencies of the data lines L1, L2, . . . , Li are exactly the same, assuming that it is f0 in this case, since each of the driving units X1, X2, . . . , Xi employs the same clock signal CK during the operation of data transmission. However, the same transmission frequency of the data signals D1 to Di in the data lines L1, L2, . . . , Li results in a significant EMI effect at several specific frequencies. In other words, the EMI effect primarily occurs at a fundamental frequency f0 of the transmission frequency and its integral times nxc3x97f0 where n is a positive integral.
FIG. 2 is a schematic diagram showing an EMI spectrum of the conventional LCD circuit shown in FIG. 1. Referring to FIG. 2, the axis of abscissa represents a frequency with an arbitrary unit while the axis of ordinate represents EMI intensity with an arbitrary unit. As compared with the EMI spectrum of the conventional LCD circuit, the upper limit of EMI intensity defined by U.S. FCC is simultaneously shown in FIG. 2. It is observed from FIG. 2 that the EMI spectrum of the conventional LCD circuit has several discrete peaks at specific frequencies, namely, the fundamental frequency f0 and harmonic frequencies 2f0, 3f0, . . . , nf0 due to the single frequency of the clock signal CK. For the sake of simplicity, however, only three EMI peaks are shown in FIG. 2. Among these EMI spectrum peaks, the maximum occurs at the fundamental frequency f0 and the magnitudes of the EMI peaks tend to decrease along with the increase of frequency. Due to the fundamental peak f0 and first harmonic peak 2f0 exceeding the upper limit of EMI intensity defined by U.S. FCC, the conventional LCD circuit shown in FIG. 1 has no practical use.
In view of the foregoing, the object of the invention is to provide a data transmission method for reducing the electromagnetic interference intensity of an LCD circuit. The LCD circuit comprises a pixel array, a clock signal generator for providing a plurality of clock signals, a data generator for providing a plurality of data sets, and a plurality of drivers. Each of the drivers receives a data set sent from the data generator and a clock signal sent from the clock signal generator. The data set is then transmitted to the pixel array through a transmission line in response to the clock signal. The data transmission method is characterized by the clock signal generator""s ability to generate a plurality of clock signals with different frequencies, each of which is distributed around a central frequency and varied within a bandwidth of 5% of the central frequency. Moreover, the clock signals have different frequencies from each other at a given time, and the clock signals used by two adjacent driving devices have different frequencies.
Furthermore, it is another object of the invention to provide a data transmission device for reducing the electromagnetic interference intensity of an LCD circuit, which comprises a pixel array, a controller, and a plurality of driving units. The controller provides a plurality of data sets and a plurality of clock signals with different frequencies, wherein each of the different frequencies is distributed around a central frequency and varied within a specific bandwidth, and the frequencies of the clock signals are different at a given time. Each of the driving units receives a corresponding data set from the data sets sent from the controller and one of the clock signals, and then transmits the data set through a transmission line to the pixel array in response to the clock signal, wherein the clock signals applied on two adjacent driving units of the driving units have different frequencies.